If the strength or resilience of a blood vessel wall weakens or deteriorates, as may occur with aging or disease, the force of blood flow through the vessel may cause a portion of the wall to stretch or balloon outward, causing an aneurysm. If the aneurysm is left untreated, the vessel wall may further expand and ultimately rupture, often resulting in death.
To prevent rupturing of an aneurysm, an endoluminal graft may be introduced into a blood vessel and deployed to span the length of the aneurysmal sac, thereby providing a path for blood to flow past the aneurysm. Endovascular grafts (stent grafts or endografts) include a graft fabric secured to a cylindrical scaffolding or framework of one or more stents. The stent(s) provide rigidity and structure to hold the graft open in a tubular configuration as well as the outward radial force needed to create a seal between the graft and a healthy portion of the vessel wall. Blood flowing through the vessel is channeled through the hollow interior of the stent graft to reduce, if not eliminate, the stress on the vessel wall at the location of the aneurysm. Endografts reduce the risk of rupture of the blood vessel wall at the aneurysmal site and allow blood to flow through the vessel without interruption.
Aneurysms occurring in the aorta, the largest artery in the human body, may occur in the chest (thoracic aortic aneurysm) or in the abdomen (abdominal aortic aneurysm). Due to the curvature of the aortic arch, thoracic aortic aneurysms can be particularly challenging to treat. Other parts of the vasculature, such as the common iliac artery which extends from the aorta, may be extremely tortuous and may present various challenges when implanting an endograft.
Endograft delivery systems may include retention elements, such as trigger wires, intended to allow selective release and deployment of portions of the endograft once an overlying outer sheath is retracted. The release of the trigger wires may cause unintended longitudinal motion, however, which results in a shifting of a portion or the entirety of the endograft. Such motion may be particularly detrimental in a curved vessel. For example, instead of having a perpendicular orientation to blood flow, the proximal (leading) end of the stent graft may become tilted at an undesirable angle that makes the endograft susceptible to leakage. Longitudinal movement of the endograft could also result in the unintended blockage of one or more major branch arteries resulting in downstream ischaemia. An improved method of deploying and positioning endovascular devices is desirable.